Apparatus for coating sheet metal



Jan. 4, 1944. J. D. KELLER APPARATUS FOR COATING SHEET METAL 2Sheets-Sheet 1 Filed Oct. 31, 1940 H W Q? 0% Q m w ,l w 5 a 5 Fig. 2A.

25 INVENTOR v (la/7n D. /\e//e/" Z2 [Z7 v m M 46% Jan. 4, 1944. J. D.KELLER 2,338,438

APPARATUS FOR COATING SHEET METAL Filed Oct. 51, 1940 2 Sheets-Shet 2INVENTOR (70/70 0. Kefler Patented Jan. 4, 1944 UNITED STATES PATENTOFFICE APPARATUS FOR COATING SHEET METAL John D. Keller, Pittsburgh,Pa., assignor to The wean Engineering Company, Inc., Warren, Ohio, acorporation of Ohio Application'october 31, 1940, Serial No. 363,652

(Cl. ill-12.5)

4 Claims.

This invention relates to the coating of sheet or strip metal and,particularly, to the tinning of steel sheets.

It is desirable for various reasons that the protective coating of tinapplied to steel sheets or strip be as thin as possible. One of thesereasons, of course, is the cost of the tin itself. Another reason isthat a thin coating exhibits better adherence than a thick coating underdeformation of the coated material.

It is the general belief that the tin coat on a steel sheet includes abottom alloy layer and an outer layer of tin several times thicker thanthe alloy layer. Attempts have been made heretofore to reduce thethickness of the tin layer by increasing the pressure exerted on thecoated strip by the exit rolls of the conventional tinning apparatus. Ithas been found, however, that when the adjustment of the exit rolls issuch as to reduce the amount of tin applied to the sheets below about1.35 pounds per base box, the surfaces of the tin sheets are notuniformly bright in appearance, but, instead, are dull and streaky. Thiscondition, known as scruff streaks or bands, appears to be the result ofwiping off the tin layer clear down' to the alloy layer. Regardless ofits cause, it precludes the sale of the coated sheets as prime material.For this reason, it has been generally believed that the thickness ofthe tin layer cannot be reduced much below that corresponding to a.total weight of tin per base box of about 1.35 pounds.

I have invented a novel apparatus whereby the thickness of the layer ofpure tin formed on steel sheets or strip by passage through a bath ofmolten tin or by some other method of applying molten tin may be reducedconsiderably below that usually obtained heretofore, without producingscruff streaks. In a preferred embodiment and practice of the invention,I subject the material emerging from the bath of molten tin to theaction of a pair of wiping members each including a flexible wall. I amthus able to exert enough pressure on the emerging sheet to wipe offmore of the excess tin than it has been possible to remove heretoforebut at the same time, I avoid solid contact between the wiping membersand the material and thereby prevent removal of the tin clear down tothe alloy layer which would produce scruff streaks as explained above.The wiping surfaces are preferably urged against the coated sheetpassing therebetween under fluid pressure which can be accuratelycontrolled and is uniform at all points.

The wiping members are immersed in a palm oil bath floating on the tinbath, as in the conventional tin pot. The palm oil being atsubstantially the same temperature as the molten tin, keeps the tincoating on the sheets or strip fluid while it is subjected to the actionof the wiping members. The latter may take the form of hollow rollshaving their bodies formed of thin, flexible material or may beconstituted by elongated box-like members having one wall composed ofsuch material. Further details of the apparatus of .my invention willbecome apparent during the following complete description andexplanation which refers to the accompanying drawings illustrating atypical form and practice. In the drawings:

Fig. 1 is a longitudinal central, vertical section through a tin potwhich is largely of conventional design but is modified to embody myinvention;

Fig. 2 is a portion of Fig. 1 enlarged considerably to illustratediagrammatically the manner in which the apparatus functions to removeexcess tin;

Fig. 2a is a plan view of the wiping rolls and backing rolls therefor;

Fig. 3 is a view similar to Fig. 2 showing a modified construction;

Fig. 4 is a similar view showing a still further modification; and

Fig. 5 is a diagram of the piping employed in connection with the.modification of Fig. 4.

Referring now in detail to the drawings, a tin pot I0 is largely ofconventional construction, including feed-in rolls ll, l2 and I3 andguide rolls l4 journaled in spaced side frames IS, the side frames I5being removably disposed in the entering end of the pot l0.

In the exit end of the pot l0, side frames l6 are disposed having feedrolls l1 journaled therein. Wipers ll engage the rolls I! to remove anysolidified particles or tin-iron crystals which may adhere thereto. Acurved guide plate l8 extends through an opening in the center wall [9of the pot to direct a sheet from the rolls l3 to the rolls I1. Abovethe'roll I'I, wiping rolls 20 are disposed in pairs, being journaled inthe side frame IS. The rolls 20, as more clearly shown in Fig. 2,comprise body portions 2| having end closures 22 secured thereto. Theend closures have bearing trunnions 23 projecting therefrom.

The body portions 2| of the rolls 20 are composed of thin-walled tubessufficiently flexible to be deformed, as shown, under the wipingpressures exerted on the sheet metal emerging from the coating bath, asindicated at 24. To permit this deformation, the rolls are preferablyconstructed as shown in Fig. 2a, the end closures 23 being smaller thanthe roll bodies and the latter being contracted adjacent their ends.

Backing rolls 25 are journaled in the side frame l6 and engage the bodyportions of the'rolls 2G. The backing rolls on one side of the wipingrolls are journaled in bearing blocks 25 adjustable relative to the sideframes by screws 21. 7

One of the rolls of each pair has a gear 28 thereon and is driven by amotor (not shown) through gears 29 and 30, the latter meshing with oneof the gears 28. The backing rolls may also be driven if desired. Therolls l1 preferably have a separate drive including a gear 3| mounted onone of the rolls and a gear 30a meshing therewith driven bya suitablemotor. This permits the rolls 20 to be driven at a peripheral speeddifferent from that of rolls I! if desired.

Above the wiping rolls, the apparatus i largely of conventionalconstruction including converging guides 32, traction rolls 33 and adeflector 34. The emerging sheets are finally de-' livered down a chute35 to suitable apparatus for further processing. Rolls 33 may be drivenat a surface speed differing rolls 20, if desired.

The level of molten tin two sides of the pot II) at about the elevationsindicated by chain lines 36. The level of the palm oil in the exit endof the pot is s milarly indicated at 37. The entire pot is disposed in asuitable setting 38 which may be of conventional construction. Animmersion heater 39 is disposed in the entry end of the pot.

In order to cause the rolls 20 to exert suflicient pressure on theemerging sheet or strip 24, to remove the desired amount of surplus tintherefrom, I provide connections 40 cooperating with 'the bearingtrunnions 23 to supply fluid under pressure to the interior of thewiping rolls. The bodies of the rolls 20 are, of. course, fluid-tightwhereby the pressure exerted on the sheet may be controlled by varyingthe pressure of the fluid on the interior of the roll bodies. Thispressure,

is maintained in the from that of the furthermore, is uniform throughoutthe length of the rolls.

Referring now particularly to Fig. 2, the sheet 24 as it leaves the tinbath carries an excessively thick adherent layer of molten tin 4|. Theflexible-walled tubes may be made of very thin metal such as stainlesssteel or of a rubber composition suitable for withstanding the action ofthe temperature and the oil. The rolls 25 are preferably, but notnecessarily, composed of non-tinning metal.

As the sheet or strip 24 ascends between the roll 20, the excess tin iswiped oil. as indicated at 43 and the strip emerges from the nip of therolls with a very thin coating of tin indicated at 44. As clearly shownin Fig. 2, the rolls 20 do not make mechanical contact with the sheet orstrip. At the same time, the pressure of the fluid such as air or oil-on the interior of-the rolls 20, may be regulated to equalize the fluidpressure exerted by the molten tin adhering to the sheet, for anydesired thickness of tin coating on the finished sheet. The molten tinacts like a lubricant to maintain separation between the sheet and therolls, the actual separation and hence the final thickness of the tinlayer depending on the pressure maintained within the rolls 20 and theadjustment of the backing rolls '25.

Fig. 3 illustrates a modification wherein the rolls 20 are replaced byelongated box-like ento the other as by screws such as those shown at21. The thickness of the tin coating on the finished product, however,is pref- It will be apparent that the rolls 20 and the box-like members45 serve to wipe oil excess tin nated.

Fig. 4 illustrates a further modification generally similar to that ofFig. 3, except that the flexible walls 46' of the box-like members 45'have slots 47a therein and conduits 48 extending therealong throughwhich hot palm oil may be discharged onto the sheet emergence from thepot, and means mounting said r the sheet metal through the bath, saiddevice comprising a pair oi wiping members above the bath between whichthe sheet metal passes alter emerging from the bath, at least one ofsaid wiping members being a roll having a body presented to the emergingsheet metal and composed of a tube of flexible metal deformable underthe pressure or the molten coating metal adhering to the emerging sheetmetal, and means mounting said roll for rotation at a peripheral speeddifierent from that of the feed rollers.

,3. A device for removing excess coating material, for use in anapparatus for coating sheet metal including a tank for holding a bath ofliquid coating material, and feed rollers for passing the sheet metalthrough the bath, said device comprising a pair of wiping members abovethe bath between which the sheet metal passe after emerging from thebath, at least one of said wiping members being a roll having a bodypresented to the emerging sheet metal and composed of a tube of flexiblematerial deformable under the pressure of the coating material adherinto the emerging sheet metal, and means mounting said roll for rotationat a peripheral speed different 5 from that of the feed rollers.

4. A device for removing excess coating material, for use in apparatusfor coating Sheet metal including means for conveying the sheet metaland means for forming a coating of liquid material thereon, said devicecomprising a pair of wiping members between which the strip passes aftertraversing the coating apparatus, at least one 01 said wiping membersbeing a roll having a body presented to the ongoing sheet metal andcomposed of a tube of flexible material deformof the liquid coatingmaterial adhering to the sheet metal, and means mounting said roll forrotation at a peripheral speed different from that of said conveying 20means.

JOHN D. KEIJLER.

